DEPENDENCE OF THE ABSOLUTE RATE-CONSTANT OF AN ELECTRODE PROCESS ON THE METAL NATURE - ELECTROREDUCTION OF THE CR(3+) ETHYLENEDIAMINE TETRAACETATE ON HG, BI, AND CD AND ITS ANALYSIS IN THE CONTEXT OF THE CLASSICAL APPROACH

The electrochemical behavior of Cr(3+) ethylenediamine tetraacetate ([ CrEDTA](-)) on Hg, Au(Hg), Bi, and Cd electrodes is studied using the polarographic and rotating disk electrode techniques. The electroreduc tion of this complex in a buffer acetate solution (pH 6.2) on the meta ls under study is shown not to be complicated by chemical or electroch emical side processes. The absence of specific adsorption of EDTA-cont aining species on polycrystalline Cd is proved by the measurements of differential capacitance on electrodes with renewable surface in Na(2) H(2)EDTA solutions. By comparing the experimental data in the framewor k of the classical theory of slow discharge, with due allowance for th e reaction center localization at different distances from the electro de surface, the rate constant of the ([CrEDTA](-)) electroreduction is found to vary in the Au(Hg) > Bi > Cd sequence; the variation can be as large as 2.5 orders of magnitude. A conclusion is drawn that the re action studied is nonadiabatic, at least, on Cd.